* Core 2.6.0+ fixes

* fix env -> config, run travis04 job

* don't duplicate free heap in frag data, use single stats struct

* fix dtostrf warnings, bump buffer sizes

* ...and even less words for fragmentation stat

- update every dynamicjsonbuffer with fixed size constructor argument
- change to ws callback registration to use a class builder (just cosmetic)
- test multiple ws data callbacks for each module
- remove some of the static strings in favour of ws data callback
- improve sensor ws callback data size, remove duplicated strings
- use static buffer in wsDebugSend
- postpone wsSend until loop, implement wsPost to allow other modules to queue message callbacks. remove Ticker based ws callbacks for data
- update WebUI files

* Thingspeak: async client fixes

- remove memory management in async client callbacks
- instead of global one, reference asyncclient from callback argument
- transfer temporary data-buffer to the global scope, avoid accidental String copy
- implement strnstr to search onData payload

* fixup format strings

* update retry time each attempt

* start with default attempts value

* trying to work with lwip2-536

* count time from last request

* promptly run flush

* send all ws config at once on start
* reduce ws json overhead by creating message buffer manually
* use k:[values] instead of k1:value1, k2:value2 etc. for lists